The shark (aka "JAWS" or "Bruce") depicted as the main antagonist in the Jaws film franchise, was the collective name for a reoccuring group of mutated Great White Sharks thought to be closely related genetically.
Based on eye witness accounts during the infamous first "Amity Incident", a tremendous great white shark was purportedly deemed responsible for an onslaught of attacks during the summer of 1973.
This particular incantation of the shark was depicted in the film Jaws released in 1975. In addition, there were slightly similar looking designed sharks depicted in follow up sequels (J2, J3D, and JTR respectively). However, the shark design as depicted in Jaws, is by far the most respected variant among aficionados of the film franchise.
Interestingly, it has never been agreed upon as to the official name the shark should be called. Casual fans of the film franchise in general tend to call the shark "JAWS", which is actually something of a misnomer considering there were different sizes and shapes of sharks featured in each of the four films in the franchise.
Because the shark was originally called 'Bruce' by film crew members in reference to Steven Spielbergs lawyer, Bruce Raynor, knowledgable fin fans tend to prefer using this as an official moniker.
Because the great white shark depicted in Jaws did not appear to look like a standard atypical great white shark, it has been suggested that this shark was in fact a mutated beast rather than a genetically perfect Great white shark specimen. This would also account for its maniacal personality and traits depicted in the film in so far as outward rogue behavior.
In Jaws, Bruce was destroyed by a compressed air tank during a sea battle led by APD chief Martin Brody, Oceanographer Matt Hooper, and Sea captain Quint. In reality, no evidence of the shark's remains have ever been found and this particular shark has yet to be seen again. A hollow, static copy of "Bruce" from the film was discovered in a junkyard years later, and is in essence a fourth "Bruce" pulled from molds for the mechanical shark used in the production of the film. Serious fans of the film have christened this rare find, "Junkyard Bruce", or JYB.
Proponents believe this shark as well as the other sharks depicted in the sequels possessed supernatural powers and could not have been destroyed, in much the same way Jason in the "Friday the thirteenth" film series could not. There are also rumors that pagan worshipers who believe there is a direct relation to the occult, make midnight trips to the site of the junkyard where the current last remaining 'Bruce' shark (JYB) exists. There they purportedly sing sea shanties and drink apricot brandy hoping to re-awaken the beast.